Round Wooden Hot Tub Buyers Guide-Hot Tub FAQs
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Hot Tub Frequently Asked Questions - Find Answers before you Buy a Hot Tub or Spa!

Information on Hot Tub & Spa Construction, Hot Tub & Spa Pumps, Heaters and Filters

What styles of hot tubs and spas are there?
What is a portable spa?
Which is more comfortable, hot tub or spa?
Why do some spas have molded seats and loungers?
What kind of seating should I look for?
Where should I put my hot tub?
How are spas constructed? 
Does wall thickness affect spa durability?
How are Hot Tubs built?
What is a PVDF interior?
Are there any advantages of a hot tub over a spa?
Can we create your own hydrotherapy system?
How can I recognize a good quality hot tub?
What kind of covers are available and how do they work?
How many jets do you need for a good massage?
Why do we have a pump on hot tubs and spas?
Does it cost a lot to run the pump?
What kind of filters are used?
How long does it take to heat up a Hot Tub and what does it cost?
What styles of hot tubs and spas are there?
Hot tub, spa, whirlpool, Jacuzzi, jetted bathtub. What do these terms mean? Many people use them interchangeably. Our buyer’s guide defines a hot tub as a deep wooden tub and a spa as a shallow, molded acrylic vessel. Both hot tubs and spas share the same hydrotherapy jets, heater, and circulating and filter equipment.  The terms whirlpool and jetted bathtub mean the same thing. They are deeper than normal bathtubs and have hydrotherapy jets. Most of them don’t have their own heaters, and none of them have a circulating and filter system. A whirlpool or jetted bathtub is usually installed in the bathroom and connected to city sewer and water; you drain the tub when you’re done; you can use soap. You don’t save water or heat—it all goes down the drain.  Jacuzzi is a trade name for a company that manufactures spas and whirl-pool bathtubs; it isn't a special kind of spa. Great Northern® is a registered trade name for our company. We invented the Rubadub Tub™ Hot Tub, OpuSpa™ Hot Tub and the Roll-Up® Cover.
What is a portable spa?
Portable spas have built-in (also called self-contained) equipment. They look like appliances. Like other hot tubs and spas, they have self-circulating systems. Portable spas appeal to people because it seems you can just buy it, plug it in, and go. No electrical hassle, no construction. The heaters on portable spas have about the same power as a hairdryer, only 1500 watts of output. Imagine heating 250 gallons of water with a hairdryer! In many cases turning on the pump that powers the jets turns off the heater. The name “portable” is somewhat misleading with some "portable spas" weighing 400–800 pounds empty!
Which is more comfortable, hot tub or spa?
Comfort and water depth are related. When you’re in water up to your neck, you’re comfortable. You have never been uncomfortable in a pool, because of its depth. The same thing is true in deep hot tubs. If the water is three to four feet deep, you will be comfortable. You don’t need to lay down trying to get comfortable.
Why do some spas have molded seats and loungers?
Molded seats and loungers have a lot of dazzle and eye appeal. They look so comfortable! Be careful about buying a highly stylized spa with arm rests, bucket seats, or other form-fitting shapes. Why? Bodies! We’re tall, we’re short, we’re big, we’re little. If a bucket seat fits one person, it’s much too small or large for someone else.  Beautifully molded loungers look as if they’re really going to support your back and be extra comfortable. Remember, water supports you! Maybe the spa is so shallow you need to lie down to be covered in water. Your body weighs only four to five pounds in the water. It takes just a pound or two of jet pressure or bubbles to lift you out and float you away. Some manufacturers try to eliminate float-away problems by making stirrups or recesses for your feet and arms. You wedge your heels in, and you wedge your arms in, and there you are, all wedged in, ready for ...comfort? Loungers also take up so much space that they limit the number people who can use the spa at one time.
What kind of seating should I look for?
The most comfortable and convenient hot tubs and spas have barrier-free seating. If you have a lot of friends, they can slide over and make room. If you buy one of our Rubadub Tubs™, you can have the seats installed at different heights too, they’re individually adjustable at any time. Regardless of your height you will have water over your shoulders!
Where should I put my hot tub?
 People with outdoor tubs usually install them close to the garage or house so they can keep the equipment in a heated area. One consideration in choosing a location for the tub or spa is ease of installation. Because spas are molded in one piece, they have some indoor installation limitations. Some spas are designed to go through standard doorways. Maximum spa diameter can’t exceed doorway height and width. Some spa shells are 61/2 feet across and approximately 28–29 or 34–35 inches deep. Measure carefully! It is impossible to get standard size spas up or down stairways. A two-person spa may go through the door, but it will be tight.  If you can find a spa that fits into your house, be sure it’s still large enough to give you the leg room and depth you need. Unfortunately, many spas that fit through the doors and around the stairways are no bigger than a two-person bathtub. Remember! Depth is everything. Consider putting the spa outside or buying a Rubadub Tub™. Our Rubadub Tub™ Hot Tubs easily go through doorways. There in an easy to assemble kit form and easy to move at any time in the future.
How are spas constructed? 
Most manufacturers use the fiberglass lay-up method of spa construction. This manufacturing method combines layers of polyester resin and glass fiber. A heated acrylic sheet is placed over a spa-shaped vacuum mold. Air is drawn out through hundreds of small holes. When the acrylic cools, they remove it from the mold and reinforce the underside of the spa with a resin and chopped fiberglass mixture. This polyester resin and glass combination can lead to a common problem—acrylic blistering. Blisters occur because of a chemical reaction between moisture from the tub and the polyester resins used in the reinforcing process. Many spas have been ruined because of blisters. Spas made from polyester resins not are blister resistant. Their finish and structure warranties are separate. The salesman points out the structure warranty because it is usually 10–15 years. Many times he won’t mention that finish warranty is only 1–3 years. You could have a blister problem in as little as one year!  Great Northern® Hot Tubs don’t have this blistering problem.
Does wall thickness affect spa durability?
The acrylic provides color, not structure. We measure durability by weight and the thickness of the fiberglass, not thickness of the acrylic. The acrylic covering is at most 1/8 inch thick and tapers to 15 or 20 thousandths of an inch in the foot well of the spa. Water is heavy. Water in a spa can weigh one or two tons. What happens when you fill a thin walled spa with water? The water pushes down and gradually bends or breaks the spa. To compensate for the lack of strength in a thin-walled spa, some manufacturers fill the underside with urethane foam. Others require sand or a wood structure underneath the spa. Sand or foam provides support under the benches or seats, lounger area and step. Portable spas depend on the wooden skirt and total foam fill to support the water weight. Unfortunately servicing plumbing leak is nearly impossible. Just look at Craigs List. There's thousands of these leakers for sale.
How are Hot Tubs built?
The art of wood tank building goes back to the fifteenth century. People built barrels and tanks to hold liquids. We build hot tubs the same way medieval craftsmen built their tanks and barrels. Barrels, wooden tanks, and hot tubs are built from curved pieces of wood called staves. Craftsmen assemble the staves and place metal hoops around them to hold the staves in place. At Great Northern, we make hot tubs out of redwood or cedar. We coat our hoops with plastic to eliminate rust. Back in the 60s hot tubs were made out of old wine vats or 500-gallon water tanks. The tub becomes watertight when the wood saturates, swells, and seals. Wooden vessels have always been popular with people who love depth and leg room. All-wood tubs are no longer as popular as they once were since all-wood construction requires clean, knot free heartwood from old growth trees. Who wants to sacrifice beautiful old trees to make hot tubs? You can get the benefits of a traditional all-wood tub (leg room, depth, and portability) with a modern, plastic lined tub. The best known lined tub is the Rubadub Tub™. Great Northern® Hot Tubs, a pioneer of the hot tub and spa industry, created it in 1978. These tubs are easy to clean and have the same hydrotherapy jets and equipment as spas.
What is a PVDF Interior?
No. The interior finish on the Rubadub Tub® is made from PVDF, an easy-to-clean industrial tank lining material designed for high-temperature service. Its semi-gloss finish resists chemical and weather damage just like acrylic. Many people mistake PVDF for pool vinyl. Pool vinyl does not hold up to the high water temperature you have in hot tubs. BEWARE! Some manufacturers use vinyl liners in their hot tubs. The life expectancy of these liners is only 1–2 years. Our tub and liner carry a Ten Year Limited Warranty - the longest in the industry!
Are there any advantages of a hot tub over a spa?
Yes! There are several reasons you might want a Rubadub Tub® instead of a spa. Here they are:
You can install a Rubadub Tub® anywhere. Because Rubadub Tubs® are not molded in one piece like a spa, you can have a large, deep Rubadub Tub® anywhere you want! The Rubadub Tub® come in a package that fits down the stairs, through the door, and even through the windows! The Rubadub Tub®, once assembled, can be moved indoors or out as the season requires, or left outdoors for year round use - even harsh winters! Its flexible, lightweight construction allows it to be moved anywhere easily!
Can we create your own hydrotherapy system?
Where does your back hurt the most? How about that neck strain? You can position the jets in your tub at the best height for your aches and pains. The Rubadub Tub® allows you to place jets where you need them. If you want one jet on the small of your back and another between your shoulders, just install two jets vertically. If you want more jets, you can have them. You can have as many jets as you want, it just takes a larger pump to power them. Call with your specific questions. 763-566-3623

You can have any size tub you want. If you want a custom-size tub, a Rubadub Tub® is the easiest, most economic way to get it. All Rubadub Tubs™ are made one at a time, so ordering an extra large or extra small tub is easy. Almost any size is possible. We have built tubs as small as 30 inches around by 30 inches high for one person, and as large as 28 feet in diameter for ski resorts.
How can I recognize a good quality hot tub?
Quality hot tubs have the following characteristics. They—
    • Are deep enough for soaking (35 to 44 inches);
    • Are lined with PVDF for long life and easy cleaning;
    • Are built from high quality redwood or cedar;
    • Have poly-coated hoops to prevent rust; and
    • Look like high quality furniture.
What kind of covers are available and how do they work?
To operate your hot tub or spa safely and efficiently, keep it covered. There are three cover types: floating thermal insulator, Styrofoam hard spa covers, and structural. Floating thermal insulators float on the water’s surface. There are two types, bubble blanket and micro cell floating blanket. Both are lightweight, inexpensive, and stop surface evaporation, a major source of heat loss. You can use them indoors year round or outdoors during the summer. Neither type prevents people or animals from falling into the water. Styrofoam hard spa covers are made from three-inch Styrofoam wrapped in Naugahyde or vinyl. They are popular despite these disadvantages: They become waterlogged easily. A waterlogged cover is difficult for one person to lift and has substantially reduced R-value. These covers break so easily, children have fallen through them and drowned. Life expectancy is only one to three years, heat loss associated is monumental. Structural covers are constructed from solid wood, or a other strong material. Be wary of plastic covers because they warp in the sunlight. Solid wood covers are strong, but heavy, awkward, and bulky. Another type of structural cover is the rolling cover. Great Northern’s Roll-Up® Covers are made from solid wood slats bonded to insulating, flexible backing. The are strong, compact, and easy to use. You don’t have to lift them, just roll them up. Roll-Up® Covers retain their R-value because they don’t waterlog. These covers keep children, pets, dirt and debris out of the tub while the keep heat and moisture in. If you have a particularly inquisitive child, you can secure the Roll-Up® Cover with a hasp and lock. And only the Great Northern® Roll-Up® Cover features a Ten Year Limited "won't waterlog" Warranty - longest in the industry!
How many jets do you need for a good massage?
Many people think the more jets you have, the better your massage. This is not necessarily true. We also have to look for a balanced relationship between number of jets, jet size (nozzle diameter), and pump size. When you’re looking at the confusing panorama of jet offerings, it’s hard to determine which of them is best. Keep this simple thought in mind: The only jet that does you any good is the one aimed at your back. The real questions are “How many people use the tub at the same time?” and “Do those people each need their own jet?”. Any jet not on somebody’s back is wasted. Don’t buy more jets than you need for the number of people in your tub. Some manufacturers offer many jets instead of fewer high quality ones. In most cases, you can’t use all the jets at once because the pump is not big enough to handle them. This type hydrotherapy system includes a director valve that you use to select one group of jets at a time! They don’t all operate at once. Large-nozzle jets permit more water to flow than small jets. More water flow means a firmer massage. A spa with many small jets could have the same massage action as a spa with fewer large jets. You need to compare total diameters of all jets in relation to the pump size. A large jet with 15–20 GPM (gallons per minute) needs 1/4 to 1/2 Hp to produce massage action. If you increase the number of jets, you must also increase pump size or decrease jet size to get proper massage action. Some manufacturers try to fool you into thinking their spa has increased hydrotherapy action because it has many jets. Their claim is true only if total nozzle diameter and pump size are larger than comparison models. Great Northern® uses very large jets and Monster Jets are also available.
Why do we have a pump on hot tubs and spas?
Pumps in hot tubs and spas have two functions: Circulation of  water through the filter and heater and to power the jets. Most hot tubs and spas use two-speed pumps; the same pump circulates water and powers the jets. On low speed these pumps use as little as 150–170 watts and cost only few dollars per month.

The bigger the pump, the more power in the massage, right!  Wrong. What gives a firm massage then? Large volume jets. The larger the jet nozzle , the higher its GPM rating. We determine a pump’s size by adding the total nozzle area of the jets its expected to power. Because there are so many different sizes of hydrotherapy jets, there is no hard and fast rule concerning pump size. In general, large jets (15–20 GPM) require 1/4 Hp per jet.  Manufacturers often use two or more pumps to power individual groups of jets if total jet area is extremely large. This practice generally saves money for everybody. We match pumps to the size and number of jets they are expected to run. Once the hydrotherapy system has been designed, increasing horsepower has no benefit on jet action. Bigger pumps only operate more jets, they don’t increase pressure! If you need more vigorous hydrotherapy action, use high GPM jets. Expect to pay more for a large number of high GPM jets and the required larger pump.
Does it cost a lot to run the pump?
Unfortunately for the spa industry, pump manufacturers have moved to inexpensive, inefficient pumps. The result is higher operational cost for consumers. For example, in the late 70s, a 1 Hp model consumed 11 amps. Over the years (because of cost cutting measures in the motor) the same model pump today consumes 15.5 amps. That’s an additional 1/2 kW per hour! Great Northern uses only energy efficient pumps. For example, our 3 Hp pump draws a approxmately 12 amps on high speed and only 170 Watts on low speed. Our Advice: Don’t specify a big pump for your spa just because it’s bigger. If you want more vigorous hydrotherapy action, ask for large-volume jets and an appropriately sized pump. If you’re still in doubt, call us.
What kind of filters are used?
Three kinds of filters are used in the swimming pool, hot tub and spa industry. Diatomaceous earth (DE), sand filters, and cartridge filters. DE and sand filters are used in cool-water pools and are not suitable for hot tubs and spas.  Hot tubs and spas use cartridge filters made of non-woven, spun-bonded, polyester fabric. Avoid filters made from paper or cotton-paper blends because you can’t clean them. They must be replaced when dirty. Polyester cartridge filters are made from two or six ounce fabric. There are two filtration methods available—suction and pressure. In the suction method, water from the tub is sucked through the filter to pump, heater, and jets. Sometimes the filter sits right inside the hot tub or spa. Suction filtration requires about four times as much filter area as pressure filtration. If you don’t have a large filter, you have to clean it often. On some systems, a dirty suction filter can cause such flow restriction that there may be damage to the pump or heater. This filtration method is cheaper than pressure filtration because it does not require an expensive housing to hold the filter cartridge. This method is used on most spas.

Pressure filtration is more expensive, but safer for the equipment and easier to maintain. The filter sits in a pressure housing located near either the tub or pump. A good six-ounce polyester fabric in a well spaced and sized filter affords good element life, excellent filtration, and little possibility of damage to pump or heater at reduced water flow. Great Northern® recommends pressure filtration. However, suction filtration is acceptable on budget sized and priced tubs.
Manufacturers determine filter size by examining two factors—bather load (number of people, how dirty they are, frequency of use) and circulating pump volume. If you had a very large pump, perhaps you‘d need a 100 square foot or larger filter. (This is large and expensive!!) If an average family used this large filter, they’d need to clean it only once a year. A more reasonably sized 25 square foot filter requires cleaning every six to eight weeks.

How long does it take to heat up a Hot Tub and what does it cost?
There is no simple answer to these questions. Before we can answer them, we need to know about the beginning water temperature, heater power, heat loss, surface area, heat retention, and final use temperature. Cost of operation depends on insulation, surface area, and energy cost.

Our Advice: Get the right sized heater! The best choice for most home spas and hot tubs is a 6 kW 240V heater. Beware of 120V only plug-in spas. They have 1500 watt heaters which won’t heat your spa adequately!
Which is the most economic, energy-efficient tub? The deep, narrow hot tub (400–600 gallons) or the shallow wide spa (250 gallons)? Many people think “Of course! The spa. There’s more water to heat in a hot tub!” Not true! Hot tubs have greater thermal mass (gallons of water) than spas. They take longer to heat up, but retain heat longer. Great Northern® Hot Tubs take less energy to maintain use temperature because they have far less total surface area to loose heat through. We don’t pay to heat water! We pay to replace the heat that sneaks out the top, sides, and bottom of the spa or tub. Remember only Great Northern® Hot Tubs are insulated. With typical wooden hot tubs there is no insulation and the wood wall and floor become saturated with water allowing heat to pass through.

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Great Northern® Hot Tubs
7909 Penn Ave. North
Minneapolis, Mn 55444
763-566-3623
Fax 763-561-1491
E-Mail info@gnht.com